Advisers to charities have a troubling concern: as Americans prepare their wills, many seem to develop cold feet when it comes to providing for charitable causes.

Only 8 percent of Americans have named a charity in their wills, according to a survey released earlier this year from Indiana University's Center on Philanthropy. That's in spite of the fact that Americans are a generous lot: Two out of every 3 have given to charity in recent years, according to the same survey.

Charitable bequests are also becoming more rare. From 1998 to 2006, the estimated yearly number of people who left money to charity has dropped from 17,587 to 9,522, according to Internal Revenue Service data. Over that period, fewer estates became subject to federal tax as the threshold for taxable estates rose from $625,000 in 1998 to $2 million in 2006.

Faced with this situation, observers involved in the research are calling on nonprofits and their supporters to be more proactive. In their view, both groups are missing an opportunity to make sure an individual's resources reflect his or her deepest values long after they pass on.

"The hardest thing may be for individuals to figure out what they really, really care about and what they'd want to be supporting after their deaths," says Melissa Brown, associate director of research at the Center on Philanthropy. "But just because it's hard doesn't mean it shouldn't happen. Sometimes the hardest things we do are the most rewarding."

But other professionals are neither as shocked nor as dismayed as those who insist charities are missing the bequest boat. As they see it, donors aren't necessarily just waiting to be asked for a bequest gift. Individuals may instead be taking steps, however self-interestedly, to accomplish goals – both for this life and beyond – that reflect their values.

"Charities may be more optimistic than is appropriate," says Steve Hartnett, associate director of education for the American Academy of Estate Planning Attor­neys, a professional association. "Most clients don't want to give to charity. They want it to go to their descendants."

Bequest giving, which added about $22 billion in 2006 according to Giving USA, represented 7.8 percent of the $294 billion that Americans gave overall last year. Though that's only a fraction of the nation's philanthropic pie, bequest giving is a key vehicle by which people fund charitable organizations.

"Over 80 percent of planned gifts are through wills," says Bruce Matthews, vice president of Campbell & Company, a Chicago-based consulting firm for nonprofit organizations and commissioner of the Center on Philanthropy survey. "You can tinker around all you want with charitable gift annuities and all this stuff, but the bottom line is most of it comes through wills. Nonprofit organizations need to start from that standpoint and establish good bequest programs."

Several factors, Ms. Brown says, help explain why so few Americans have written a charity into their wills. Surveys from recent years suggest fewer than half of all Americans have any will whatsoever. Plus, those with wills routinely make their first priority to provide for dependents and other family members. Since all but the wealthiest tend to worry that shifting circumstances over time could land their kin in need, Mr. Hartnett says, many hesitate to sign a legal document that earmarks funds for other purposes.

Nevertheless, this year's Center on Philanthropy survey found that certain types of people who hadn't named charities in their wills said they would consider doing so. The most likely group was working people between ages 40 and 60 with household incomes between $50,000 and $75,000 per year. That finding tells Mr. Matthews that many in the general public crave a bequest connection but haven't found the right moment to get it done.

"There's a great opportunity for us," Matthews says.

Not everyone perceives such an unmet craving. Daniel Borochoff, president of The American Institute of Philanthropy, a charity watchdog organization, notes that donors don't receive any immediate tax write-off when they put charities in their wills. And because most estates are exempt from federal as well as state taxes, donors who name a charity in their wills usually aren't reducing the tax that their estates pay after they're gone.

In this environment, Mr. Borochoff says, more donors are taking advantage of vehicles such as charitable gift annuities.

"You can set up an annuity so that while you're alive you get an income stream from the charity, and then you get the tax benefits, too," he says. "So if you're really savvy, you're thinking about these arrangements so you can get the tax benefits before it's too late. Once you're dead, the tax benefits aren't going to be any good."

Bequest giving isn't likely to pick up anytime soon unless Congress reinstates lower thresholds for estate taxes, according to Diana Aviv, president and CEO of Independent Sector, a coalition that lobbies on behalf of nonprofits.

"Charitable bequests, which we believe to be one of the pillars of philanthropy, derived an immense benefit from the estate tax because folks would be motivated to give money to charity instead of being taxed on their estates," Ms. Aviv says. "By substantially changing the estate tax, [Congress has hastened] a drop in bequests."

Some proponents of bequest giving highlight, however, that the practice affords donors several benefits – tangible as well as intangible – even under the current tax code. Those with estates large enough to face taxation (values above $2 million trigger federal tax; amounts above $1 million incur tax in certain states) can indeed cut their estate's tax bills by naming charities in a will or trust. And anyone with charitable intentions gains a measure of control.

Without an immediate financial payoff to encourage the donor in most cases, many put off last-will-and-testament decisions. People get overwhelmed by the prospect of "playing God" in deciding who gets what, Borochoff says, and they also resist confronting mortality.

Yet donors who do take the step of putting a charity in their wills enjoy the fruits of having deepened a relationship with an organization since, as Brown says, "you now have a stake in the organization's health and welfare for the long term, even after you're no longer around." And, she adds, because the process raises the question, "what's most important to me?," donors who take the step inevitably grow in a personal way as a result.